TM 11-5840-281-35/1
identical i-f preamplifiers (Intermediate-Frequency
plifier AM-3337/TPN-8 assemblies are provided by the
Amplifier AM-3337/TPN-8 assemblies).
stc unit.
(1) The dual crystal outputs of the mixer
(1) I-f gain voltage is supplied from IF GAIN az
assembly are transformer-coupled to the grid of tube
control R617A and IF GAIN el control R617B. These
V1301 through the wideband input coupling circuit. The
voltages are switched by az-el switching relay K4015 on
dc component of the crystal is coupled from input
Remote Switching Control C-6989/TPN-18 in unison with
transformer T1301 through the 1c filter networks to XTAL
the radiating antenna and applied through MAX SENS
CUR switch S104 on the control panel of Radar
control R4079 to the stc unit on a single input line. The i-f
Receiver-Transmitter RT-818/TPN-18. Each 1c line from
gain voltage is applied to cathode follower V3902A after
transformer T1301 is grounded through 100 ohms of
filtering by input circuit components; from cathode
resistance except when XTAL CUR switch 8104 is
follower V3902A, it is applied through isolating diodes to
positioned to monitor the current of one of the mixer
cathode followers V3903A and V3903B. Cathode
crystals. When monitoring the crystal current, the 100-
follower V3903A provides gain control voltages for sum
ohm resistor in that line is replaced by the equivalent
channel Intermediate-Frequency Amplifier AM-3337/
resistance of XTAL CUR meter M101 in series with a 7
TPN-8, and V3903B for the difference channel.
hm resistor.
When STC switch S604 is placed to OFF, cathode
(2) The input circuit consisting of choke L13101,
followers V3903A and V3903A and V3903B supply a
capacitor C1337, and transformers T1301 and T1304, is
fixed gain control voltage to Intermediate-Frequency
tuned to provide an input bandpass of 25 MHz to the
Amplifier AM-3337/TPN-8. With STC switch S604 placed
conventional low-noise, grounded-grid, amplifier stages
to ON, the i-f gain control voltage is modified by the stc
of cascode tubes V1301 and V1302 of Intermediate-
unit to supply an exponential volt- age to Intermediate-
Frequency Amplifier AM-3339/TPN-8. Capacitor C1303
Frequency Amplifier AM-337/TPN-8 that increases the
and choke L1303 provide neutralization for tube V1301.
receiver section gain as the indicator section sweep time
The 60-MHz, Intermediate-Frequency Amplifier AM-
base increases in range.
3337/TPN-8 is tuned for an overall 13-MHz bandwidth,
(2) The stc voltage is developed by the dis-
with a maximum gain of approximately 21 dbm. The grid
charging of capacitor C903 through STC SLOPE
bias voltages of tubes V1303 and V1304 are varied
control R3911. Prior to the triggering of monostable
together to provide control of the receiver gain. Individual
multivibrator V3901, capacitor C3903 is charged to about
gain controls IF GAIN AZ R617A and IF GAIN EL B617B
--30 volts through the conducting side of tube V3901.
(sum channel), and EL TARGET R620 (difference
When triggered by the pretrigger pulse, tube V3901
channel), located on Control-Indicator -6988/TPN-18, are
develops a positive gate of about 500-_sec duration.
switched in the proper sequence to provide optimum
During the gating period, capacitor C3903 discharges to
display for azimuth and elevation signals. These signals
zero through resistor R3911. The setting of resistor
are applied to Intermediate-Frequency Amplifier AM-
R3911 determines how long capacitor C3903 will take to
3337/ TPN-8 through the c unit.
discharge. The resulting exponential vol- tage is applied
(3) The output i-f signal of the difference channel
through cathode followers V3902B, V3903A, and
Intermediate-Frequency Amplifier AM-337/TPN-8 is fed
V3903B to Intermediate-Frequency Amplifiers AM-
to log Intermediate-Frequency Amplifier AM-338/TPN-8.
3337/TPN-8. The amplitude of the tc waveform super-
The output i-f signal of sum channel Intermediate-
imposed on the output gain control voltages is adjusted
Frequency Amplifier AM-337/TPN-8 is fed through a 160-
by controls a 3913, SUM STC GAIN, and R3914, DIFF
foot coaxial cable delay line to Intermediate-Frequency
STC GAIN.
Amplifier AM3339/TPN-8. This delay provides
(3) The gain in the difference channel is con-
coincidence of the sum channel i-f signal and the
trolled by EL TARGET control R620 on Control- Indicator
difference channel iagc pulses in Immediate-Frequency
C-6988/TPN-18. This control increases or decreases the
Amplifier AM-3339/TPN-8.
difference channel gain which increases or decreases
f. Sensitivity Time Control (STC) Circuit (Fig.
the vertical width of the die played elevation targets.
7-7 and 7-38). Sum and difference channel gain control
(4) During the azimuth scan period, the gain of
voltages to Intermediate-Frequency Am-
the difference channel is reduced to a minimum
2-18
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